It is conventionally known to pick up pulses (pulse amplitude) from image information acquired from a finger. This image information is acquired by taking an image of a finger using transmitted light such as near-infrared light. An image must be taken while a finger is maintained in a correct state to acquire correct image information.
With regard to picking up of pulses, Japanese Patent Application Laid-Open Publication No. 2007-244600 discloses including a pressurizing member to which a finger tip is pressed as well as a finger tip position stabilizing means which stably holds the position of the finger tip pressed to the pressurizing member and a finger pressure equalizing means which makes the pressurizing member freely movable with nearly equal finger pressure to stably hold the position of the finger tip and equalize a pressurizing force applied from the pressurizing member to the finger tip so as to prevent the photographing range of the finger tip and blood flow from being affected, so that the pulse wave is collected stably (Abstract, FIG. 1, etc.).
Japanese Patent Application Laid-Open Publication No. 10-155754 discloses detecting pressing of a finger with a pressure sensor; obtaining a DC component of the detected output, which is stored into a calibration table in correspondence to a pressure level; calculating a threshold as reference in the grading of sensation based on the maximum value of the pressure level and the calibration table, which is stored into a threshold table; detecting a blood stream of a finger when holding an object; and obtaining a DC component of the detected output, which is compared with the threshold in the threshold table to display sensation information indicative of the degree of the pressing (Abstract, FIG. 5, etc.).